Hazards of excessive or inadequate concentration of specific gases exist in many forms. For example, low oxygen levels may lead to asphyxiation. On the other hand, excessive oxygen levels may create a combustion hazard. However, various industrial processes require large amounts of liquid or gaseous nitrogen and oxygen. Thus, in the home health care environment, it is desirable to monitor the output of an oxygen concentrator to determine whether the output oxygen level remains above (or falls below) a predetermined minimum desired limit. In other industrial and commercial applications, it is desirable to maintain oxygen concentration between preset lower and upper limits.
Accordingly, the presence or absence of oxygen or other gaseous materials, in concentrations having specific relationships to predefined thresholds, may create a potential for serious problems.
Thus, as a safety precaution, every situation wherein excessively low or excessively high concentrations of gases (such as oxygen) may exist, requires identification and evaluation of the specific concentration. For example, a long stretch of hallway with high pressure gas lines; a room with poor ventilation and significant amounts of inert or oxygen rich gas storage, or an environment having storage areas for chemicals which can deplete or enrich the oxygen concentration therein, provide potentially hazardous environments which should be monitored.
When an oxygen hazard may exist, there is needed a drift free, long life, accurate and dependable oxygen monitoring devices.
Oxygen concentration monitors are known in the prior art. For example, one such apparatus is disclosed in U.S. Pat. No. 5,402,665 to Hart et al., the contents of which are incorporated herein by reference.
However, the apparatus disclosed therein operates to compare ambient oxygen concentration with a predetermined threshold level and to provide an indication when the monitored concentration exceeds (or falls below) the threshold. More particularly a calibration gas, having an oxygen concentration equal to a desired threshold concentration level, is used to calibrate the device in order to account for variations in the operating characteristics of the oxygen sensor used therein. A specific testing and calibration procedure is thus required and the disclosed apparatus provides an indication if the monitored concentration is greater (or less) than the desired threshold.
The patent also discloses that one or more calibration gases may be used, at respective concentrations, in order to establish various calibration threshold levels.
However, a drawback of such a device is that a plurality of specific calibration procedures must be followed in order to calibrate the device to monitor concentrations with respect to a plurality of threshold levels to be monitored. Moreover, while the disclosed device may activate an audible alarm, buzzer, or LED (light emitting diode) to indicate a relationship between the concentration being monitored and a threshold, there is no provision for indicating the actual oxygen concentration level.
There is thus a need in the prior art for method and apparatus for monitoring concentrations of oxygen using only a single calibration gas.